2. Topics to be learnt
a. Reversible and Irreversible change
b. Physical Change – characteristics , properties
c. Activity related to physical change
c. Chemical Change- characteristics , properties
d. Activity related to chemical changes
i) Burning of magnesium metal
ii) Reaction between Copper sulphate with iron
iii) Reaction between Vinegar and Baking Soda
e. Ozone layer
f. Difference between physical and chemical changes
g. Rusting of iron
h. Galvanisation
i. Crystallization
j. Activity crystallization
3. Introduction
Changes takes place around us .Some of
the changes observed by us in every day life
are:
a. Formation of curd from milk
b. Cooking of food
c. Burning of Fuel
d. Ripening of fruits
e. Drying of clothes
f. Rusting of iron
Some of these changes can be reversed
whereas some cannot be reversed by reversing
the conditions
4. Reversible Change Irreversible Change
a. The change which can a. The change which cannot
be reversed by reversing be reversed even by
the conditions is known reversing the conditions
as reversible change. is called irreversible change
b. For eg , stretching of b. Eg. Rusting of iron
rubber band , glowing burning of paper ,
of an electric bulb , cooking of food, growth of
melting of ice plants , burning of fuels
c. Reversible changes are c. Irreversible changes are
temporary changes permanent changes
5. Physical Changes
Properties such as shape , size colour and
state of a substance are called its physical
properties.
A change in which only the physical properties
of any substance get changed and no new
substance is formed is called a physical
change .
6. Big piece of paper cut into small pieces is a physical
change
7. Melting of Ice and Freezing of water are Physical
Changes
8. Characteristics of Physical Changes
1. During a physical change , only some of the physical
properties such as size ,shape , colour and state change
2. No new substance is formed in a physical
change.
3. A physical change is a temporary change .
4. Chemical composition of a substance remains
the same during a physical change .
5. No overall energy change takes place .
9. Examples of Physical Change
a. Stretching of rubber band .
b. Grinding of a substance .
c. Expansion or contraction of substances on
heating and cooling .
d. Melting of ice
e. Formation of clouds
f. Hammering of metals to form thin sheets
10. Chemical Changes
A change in which one or more new substances
with entirely different chemical composition and
properties from the original substances are
formed is called a chemical change .
11. Characteristics of chemical changes
a. During a chemical change , one or more new
substances are formed .
b. Chemical changes are permanent , thus a
chemical change cannot be reversed
c. A large amount of energy is either given out or
absorbed in the form of heat or light eg burning
of fuel produces large amount of heat . During
Photosynthesis green plants absorb solar energy
to make food .
12. d. Sound may be produced
e. A change in smell may take place
f. A colour change may take place
g. A gas may be formed .
13. Examples of Chemical changes
a.Burning of magnesium ribbon
b. Burning of coal , wood or leaves is a chemical
change
c. Explosion of a firework is a chemical change
d. When food gets spoiled , it produces a foul
smell . Slice of an apple acquires a brown colour
if not consumed immediately .
14. Aim - To Show that burning of magnesium metal is a chemical
change
Materials Required - A magnesium ribbon , thin strip of ribbon of
magnesium , sandpaper , candle
Method –
Take a magnesium ribbon about 10 cm long
Clean it by rubbing its surface with sand paper
Hold the burning magnesium ribbon at one end with a pair
of tongs and heat the other end over the flame of Bunsen burner
till it catches fire
The magnesium ribbon burns with a white dazzling flame forming
a white powder
15. When Magnesium ribbon burns in air it forms Magnesium oxide
( MgO )
2Mg + O2 2 MgO
Magnesium + oxygen Magnesium oxide ( white powder )
collect the white powder in a beaker having 20 ml of
distilled water
Stir the mixture thoroughly to dissolve magnesium oxide in
water
MgO + H2O Mg ( OH )2
Magnesium oxide water Magnesium Hydroxide
16.
17. Test this mixture of Magnesium Hydroxide formed with litmus
papers
Blue litmus paper
strip
+
Magnesium
hydroxide solution
No change in colour
of litmus paper shows
that the Solution of
magnesium oxide in
water is not acidic
Red litmus paper
strip
+
Magnesium
hydroxide solution
The red litmus paper
turns blue showing
that the solution of
magnesium oxide in
water is basic in
nature
18. Thus we conclude that
Burning of magnesium ribbon is a chemical change
MgO formed on
burning that is a
new substance
MgO when
combined with water
forms Mg ( OH) 2
that is a new
substance
19. Activity – Reaction between copper sulphate and
Iron
Aim - To show that in a chemical change , one or
more substances with entirely new chemical
composition and properties are formed
Things needed - Copper sulphate , water , a
beaker , dilute sulphuric acid , an iron nail and
test tube
20. Method –
Dissolve about a teaspoonful of copper sulphate
( blue vitriol or Neela thotha ) in about half a cup of
water in a beaker
Add a few drops of dilute sulphuric acid to the
copper sulphate solution
Blue – Coloured copper sulphate solution is obtained
21. Blue – Coloured copper sulphate solution in a
beaker + Nail or Used shaving blade
Leave the arrangement for 30 min
22. Observation
Two changes are observed
a. The change of colour of solution from blue to green is
due to the formation of iron sulphate
Copper Sulphate + Iron Iron Sulphate + Copper
Solution ( blue ) solution ( green ) brown
CuSO4 + Fe FeSO4 + Cu
b. Brown deposit of copper is formed on the iron nail
23. Conclusion - We conclude that during a chemical
change
New
substances
are formed
Change in
colour
takes place
24. Aim – To show that reaction between vinegar and
baking soda leads to a chemical change
Things needed - Two Test tubes, vinegar , baking
soda , lime water , stand , cork
25. Method -
About 10 ml of vinegar is taken in a (test –tube 1)
pinch of baking soda is added to the vinegar(test tube 1)
Hissing sound and bubbles are observed
Vinegar ( Acetic Acid ) + Baking Soda ( Sodium hydrogen
carbonate ) Carbon – dioxide + H2O+ Sodium
Acetate
CH3COOH + NaHCO3 CO2 + H20 + CH3COONa
Vinegar + Baking Soda carbon dioxide + water+
Sodium acetate
26. The gas released during the above reaction passes
through (test tube 2) having lime water .
C02 + Ca (OH)2 CaCO3 + H2O
Carbon dioxide Lime water Calcium Carbonate water
( calcium hydroxide )
27. Observation - When carbon – dioxide passes through
lime water
Lime water turns milky
Conclusion - The above reaction is a chemical reaction
28.
29. Physical Change Chemical Change
1. No new substances are
formed
1. New Substances are
formed
2. A physical change is a
temporary Change
2. A chemical change is a
permanent Change
3. A physical change is
easily reversible
3. A chemical change is
usually irreversible
4. A very little energy is
Absorbed or given out in a
physical change
4. A lot of energy is
absorbed or given out in a
chemical change
